MEMS component and method for encapsulating MEMS components

ABSTRACT

A MEMS component includes, on a substrate, component structures, contact areas connected to the component structures, metallic column structures seated on the contact areas, and metallic frame structures surrounding the component structures. A cured resist layer is seated on frame structure and column structures such that a cavity is enclosed between substrate, frame structure and resist layer. A structured metallization is provided directly on the resist layer or on a carrier layer seated on the resist layer. The structured metallization includes at least external contacts of the component and being electrically conductively connected both to metallic structures and to the contact areas of the component structures.

This patent application is a national phase filing under section 371 ofPCT/EP2013/071396, filed Oct. 14, 2013, which claims the priority ofGerman patent application 10 2012 112 058.7, filed Dec. 11, 2012, eachof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

A MEMS component and method for encapsulating MEMS components aredescribed.

BACKGROUND

An electronic component comprising a hermetically closed housing and aproduction method can be gathered from DE 102008025202 A, for example.The encapsulation method can be carried out at the wafer level. For thispurpose, firstly component structures for a multiplicity of electroniccomponents are produced simultaneously on a component wafer. On thewafer, a metallic frame is produced around the component structures ofeach component, said metallic frame enclosing the component structures.A covering film comprising at least one metal layer is then placed ontosaid frame and fixedly soldered to the metallic frame.

SUMMARY

Embodiments of the present invention specify a MEMS component and amethod for encapsulating MEMS components, which MEMS component has asimplified construction and is simple to produce.

The MEMS component comprises a substrate having an active surface, onwhich electrical component structures and contact areas for makingelectrical contact with the component structures are arranged. Inaddition, metallic structures in the form of column structures and aframe structure are arranged on the active surface of the substrate. Themetallic column structures are situated on the contact areas and projectbeyond the component structures. The metallic frame structure enclosesthe component structures on the surface of the substrate.

The component structures together with a portion of the columnstructures are arranged in a cavity that is formed and closed off by acured resist layer seated on the frame structure and the columnstructures. In this case, the resist layer can be UV-cured or thermallycured. At least one portion of the metallic structures, that is to sayat least one portion of the column structures and the frame structure,in this case penetrates through the resist layer in such a way thatthose surfaces of the metallic structures which face away from thesubstrate terminate flush with the outwardly facing surface of theresist layer. A structured metallization is provided above that surfaceof the resist layer which faces away from the substrate, or on a furtherembossing layer arranged directly above the resist layer. At leastconnection areas for making contact with the MEMS component are formedfrom said structured metallization. Therefore, the structuredmetallization is electrically conductively connected at least to thecolumn structures penetrating through the resist layer, and thus also tothe component structures.

The proposed MEMS component can be produced in a simple manner. It isalso cost-effective on account of the materials used.

The closure of the cavity is effected by means of the cured resist layerrather than by means of a solder, with the result that elevatedtemperatures, such as are required for melting solder, for instance, arenot necessary for sealing the cavity. The lowest thermal loading isobtained with the use of a UV-curing resist. Since MEMS components, inparticular, can react sensitively toward thermomechanically generatedstresses with deviation of their component properties, a componentproduced at low process temperatures can be produced with highmanufacturing reliability. The production method produces few rejectsand thereby additionally lowers the costs of the component.

The MEMS component comprises mechanically sensitive component structureswhich, for reliable operation, require a cavity housing such as is madeavailable by the invention. The component structures comprise movableparts, wherein the movement can also constitute an oscillation. Oneclass of MEMS components which preferably require hermetic cavityhousings is components which operate with acoustic waves. These can beSAW components (SAW=surface acoustic wave) that operate with surfaceacoustic waves. It is also possible for the MEMS component to beembodied as an FBAR resonator (FBAR=thin film acoustic resonator) orFBAR filter, the component structures of which comprise resonators thatoperate with bulk acoustic waves. Diverse sensors can also be embodiedin the form of MEMS components.

In one embodiment, a carrier layer is arranged above the resist layer.The structured metallization with the external contacts is then arrangedon that surface of the carrier layer which faces away from thesubstrate.

Plated-through holes are provided through the carrier layer and connectthe external contacts to the metallic structures. Electricallyconductive connections to individual column structures, to all thecolumn structures and optionally also to the frame structure can beprovided in this case.

In a simple first embodiment, the cured resist layer serves as the solecover layer of the cavity housing. In conjunction with the carrier layerarranged thereon in accordance with a further embodiment, the curedresist layer serves as connecting and sealing layer. The mechanicalstability of the cavity housing or the cover thereof can be ensuredsolely by the carrier layer. The resist layer can then be madecorrespondingly thin. It is also possible, however, to make the resistlayer correspondingly thicker and to ensure the mechanical stability bymeans of correspondingly dimensioned combinations of resist layer andcarrier layer that are coordinated with one another.

In one configuration of the MEMS component, a hermetic layer is arrangedon the rear side of the substrate, said rear side being situatedopposite the active surface of the component, and seals the componentrelative to the carrier layer. The hermetic layer therefore preferablycomprises an inorganic layer, for example, an impermeable oxide or anitride layer or, in particular, a metal layer.

A hermetic housing is obtained if the carrier layer is also hermeticallyimpermeable and has no or only a low permeability to gases, moisture orsuch liquids which could jeopardize or corrode the component structuresor which could disturb the operation of the MEMS component.

A further possibility consists in also sealing the rear side of thecarrier layer with a further hermetic layer, for example, with astructured passivation layer which is arranged above the contactstructure and in which the external contacts are exposed.

In one embodiment, the substrate is a piezoelectric wafer and thecomponent structures comprise an interdigital transducer. The carrierlayer is preferably embodied as a glass film. In a manner appropriatelymatched to this, the hermetic layer can then be embodied as a metalliclayer.

A MEMS component embodied in this way comprises an SAW component whichcan be produced cost-effectively with the glass film as carrier layerand the resist layer as connecting layer. The metallic layer as hermeticlayer yields firstly an impermeability toward aggressive environmentalconditions and secondly a shielding against electromagnetic radiation,thereby preventing an electromagnetic interaction of the componentstructures with the outside world.

A MEMS component is produced by a procedure in which electricalcomponent structures and contact areas connected thereto are produced onan active surface of a wafer. Furthermore, metallic structures areproduced on the active surface, said metallic structures comprisingcolumn structures situated on the contact areas and a frame structureenclosing the component structures, wherein the frame structure islikewise seated on the active surface of the wafer. In a further step,the surface of the metallic structures is planarized by means of asuitable method, for example by grinding away or milling.

Afterward, a carrier layer is placed onto the metallic structures withthe aid of a UV-curable resist layer and is fixedly connected thereto byvirtue of the resist layer being cured by means of UV irradiation. Byvirtue of the carrier layer being adhesively bonded with the aid of aUV-curable resist layer, a simple method for producing a cavity housingfor the MEMS components is specified, which can be carried out at thewafer level.

The UV irradiation can be carried out at room temperature, wherein thecomponent can be reliably prevented from being heated to an excessivelygreat extent. Consequently, practically all steps for manufacturing boththe component and the encapsulation thereof can be carried out atambient temperatures, such that the housing can be closed without athermal strain occurring between differently expanding housing parts inthe process. A stress-free housing guarantees that the component fixedlyconnected thereto also remains stress-free. Such a component firstly isless susceptible to damage and secondly also exhibits no alteration ofits thermomechanical and ultimately also electrical properties whichcould be associated with a mechanical strain.

In one embodiment, a further metal ply is applied on a portion of themetallic structures after the planarization. A renewed planarizationstep can then be carried out. As a result, metallic structures areobtained which have at least two different heights above the surface ofthe substrate. The upper ends of the metallic structures of each metalply lie in each case within one plane.

The carrier layer is preferably coated with the resist layer over thewhole area and then placed onto the metallic structures such that thatportion of the metallic structures which is coated with the furthermetal ply penetrates through the resist layer until it comes intocontact with the surface of the carrier layer. In this case, thethickness of the resist layer is chosen to be thicker than the height ofthe further metal ply. This guarantees that the surfaces of all themetallic structures are embedded in the resist layer, wherein only thoseportions of the metallic structures which are provided with the secondmetal ply extend as far as the carrier layer.

This embodiment has the advantage that, owing to the metallic structuresembodied with different heights, only the structures having the greaterheight can be contacted in a contacting method in a simple manner.

In a further embodiment, blind holes are produced in the carrier layerand extend through the carrier layer and the surfaces of at least themetallic structures thickened with the second metal ply are exposed insaid blind holes. For the case where all the metallic structures havethe same height, the metallic structures to be exposed in the blindholes can be freely selected.

A structured contact structure is then applied to that surface of thecarrier layer which faces away from the substrate/wafer such that it iselectrically connected to the metallic structures exposed in the blindholes. For this purpose, either an application method is chosen whichproduces/deposits a conductive contact layer in the blind holes as well.However, it is also possible firstly to fill the blind holes withconductive materials and subsequently to choose an application methodfor a contact layer or a contact structure which can be carried out on aplanar surface.

The contact structure can also be produced in a directly structuredmanner or is firstly applied as a whole-area contact layer andsubsequently structured.

The contact structure can also be a wiring structure in whichelectrically conductive connections are produced between differentmetallic structures exposed in blind holes. However, a contact structureis also possible which has external contacts arranged directly above theblind holes, in particular solderable metallic areas that are inelectrically conductive contact with the corresponding metallicstructures. In all embodiments, the carrier layer serves as anelectrically insulating interlayer between the metallic structures andthe contact structure and also as a carrier of the contact structures.In addition, the carrier layer can consist of a material having asufficient hermeticity.

In one embodiment, the UV-curable resist layer is applied to the carrierlayer over the whole area. The carrier layer is subsequently placed onthe metallic structures such that at least one portion of the metallicstructures penetrates through the resist layer as far as the contactwith the surface of the carrier layer. For the case where all themetallic structures have the same height, all the metallic structuresare introduced into the resist layer until they come into contact withthe surface of the carrier layer.

The resist layer is subsequently cured by means of UV irradiation. Afterthe resist layer has been cured, the carrier layer is stripped away fromthe resist layer. A cavity remains in which the component structuresenclosed by the frame structure are enclosed between resist layer andwafer.

In the next step, a structured contact structure is applied to thatsurface of the resist layer which faces away from the wafer such that itis electrically conductively connected to the metallic structures thatpenetrate through the resist layer and are therefore exposed.

This embodiment has the advantage that no blind holes are required forcontacting purposes, since the surfaces of the metallic structures areexposed on the resist layer. If appropriate, a uniform layer removingstep can be carried out to remove a remaining residual layer thicknessbetween the metallic structures and the outwardly facing surface of theresist layer. By way of example, a short plasma treatment suitable foretching the resist can be carried out for this purpose. By way ofexample, an oxygen plasma can be used.

In a further embodiment, a whole-area resist layer is not used. Rather,a resist layer is selectively applied to the surfaces of the metallicstructures. A carrier layer is subsequently adhesively bonded onto saidmetallic structures provided with the resist layer, wherein the resistlayer is used as an adhesive.

Since the resist layer is suitable here for adhesive bonding rather thanfor sealing the cavity, the carrier layer remains on the arrangement. Inthe next step, therefore, here as well blind holes are produced and thesurfaces of the metallic structures are exposed therein. Afterward, astructured contact structure is applied to that surface of the carrierlayer which faces away from the wafer such that an electricallyconductive contact of the contact structure with the metallic structuresexposed in the blind holes is produced.

In this embodiment, during the production of the blind holes, bycomplying with the lateral tolerance it is possible to ensure that thestructure widths of the blind holes are less than the structure widthsof the metallic structures and the cavity enclosed between carrier layerand wafer thus need not be opened.

If a method for monitoring the etching depth for the blind holes isavailable, the above-described variant with the different heights of themetallic structures can be carried out with greater lateral tolerance.In this case, however, care should be taken to ensure that the depth ofthe blind holes does not exceed the layer thickness of the resist layer,in order here as well to avoid an opening of the cavity between resistlayer and wafer.

The last-mentioned method variant has the advantage that although a highlateral structure accuracy is required during the production of theblind holes, the method is controllable in a simple manner with regardto the depth of the blind holes, since the surfaces of the metallicstructures can serve as a stop or as an etching stop.

In all the method variants, a trench pattern can be produced in theactive surface of the wafer before connection to the resist layer andthe carrier layer such that a multiplicity of component regions areseparated from one another as a result. The component structuresassigned to a respective component are arranged in each componentregion. Resist and carrier layers are subsequently applied and theresist layer is cured.

At an arbitrary stage after this method step, the wafer can subsequentlybe thinned from the rear side until the trench pattern is exposed. Thishas the effect that each component region has a substrate portioncompletely separated from the other component regions.

Besides the separation into individual substrates, the wafer thinninghas the advantage that the total height of the component is reduced,wherein the composite assembly comprising the resist layer and thecarrier layer ensures that the components is nevertheless sufficientlymechanically stable and is therefore stable to withstand both damage anddeformation. The thinning of the wafer is preferably carried out bymeans of a mechanical method, for example by means of a grinding ormilling process.

In a further method variant, the wafer or the separated individualsubstrates is or are sealed relative to the carrier layer or relative tothe resist layer from the rear side by means of a hermetic layer. Thehermetic layer is therefore applied at least to the rear side of thewafer and to the surface of the carrier layer or of the exposed resistlayer.

In one method variant, an anisotropic deposition of the hermetic layeralso leads to an edge covering, such that the hermetic layercontinuously covers the rear sides and side surfaces of all thecomponents.

In one method variant, the hermetic layer can also be applied only atthe locations at which the hermeticity of the existing housing has to bereinforced. These locations are, in particular, the surface and otherexposed interfaces of the resist layer with respect to the framestructure and with respect to the carrier layer. In this case, a methodwhich can produce a structured hermetic layer positionally accurately isused for producing the hermetic layer. A nanojet method, in particular,is suitable for this embodiment, wherein preferably metallic inks areapplied by printing/jetting. However, it is also possible for thehermetic layer to be applied by sputtering or printing using a differentmethod. Optionally, the applied structures or the layer applied over thewhole area can subsequently also be reinforced by electrolytic orelectroless metal deposition. The different methods for producing thehermetic layer can also be combined.

A better hermetic sealing by the hermetic layer is achieved ifpreviously exposed surfaces of the resist layer are substantiallyremoved. This can be carried out at a method stage after the trenchpattern has been exposed by wafer thinning. By means of a suitableetching method, through the opened trench pattern, the surface of thecarrier layer can then be freed of the resist layer situated there. Inthis case, the method can be set such that the regions of the resistlayer which function as adhesive between the metallic structures and thecarrier layer are left undamaged by the etching method. By way ofexample, an oxygen-containing plasma is suitable for etching the curedresist.

The UV-curable resist layer can be cured by means of UV irradiationthrough the carrier layer in a simple manner if a carrier layer that istransparent to UV radiation is used.

However, it is also possible additionally or alternatively to use awafer that is transparent to UV radiation. For components that operatewith acoustic waves, piezo-substrates are suitable for this purpose,which are generally likewise transmissive to UV radiation. For thevariant with a carrier layer, a thermally curing resist can also beused, wherein the wafer is then brought to a correspondingly elevatedtemperature in its entirety, e.g., in a furnace. However, it is alsopossible to place the arrangement with the carrier layer onto a heatingplate in order to bring about heating only locally.

The carrier layer can be an arbitrary thin film. It can consist of glassor comprise a glass layer. It can be a plastic film. It can be acomposite film comprising at least one plastic layer and one metallayer. In one embodiment layer, the carrier layer is provided with ametal lamination, for example with a copper lamination, and comprises aplastic film. A contact structure can be produced from such ametal-laminated carrier layer in a simple manner by means of etchingstructuring. Said contact structure can be reinforced after structuringby metallic deposition, if appropriate. It is also possible to apply aresist to the metal-laminated surface, to structure it and then toreinforce the layer in the exposed regions. After the removal of theresist, the residual thin lamination remaining can be removed byetching. In this case, the blind holes can be opened before or after thestructuring of the metal lamination. In both cases, however, it mustthen be ensured that an electrically conductive contact is producedbetween metallic structures in the blind holes and the metal lamination.This can be carried out for example by filling the blind holes withelectrically conductive material.

In the last step, the components are singulated by the carrier layerand/or the resist layer being severed between the individual components.This is preferably carried out by means of a sawing step. However, it isalso possible to perform the separation into individual components bymeans of a laser method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail below on the basis ofexemplary embodiments and the associated figures. The figures have beendrawn up merely schematically and serve solely for affording a betterunderstanding of the invention. Individual parts may therefore beillustrated with enlarged or reduced size. Therefore, neither absolutenor relative dimensional indications can be inferred from the figures.

In the figures:

FIG. 1 shows a MEMS component during one method stage after connectionto a carrier layer in schematic cross section;

FIG. 2 shows a MEMS component at the same stage in one method variant;

FIGS. 3A to 3C show different method stages during the production of analternative embodiment;

FIGS. 4A and 4B show two method stages during the production of a MEMScomponent of a further embodiment;

FIGS. 5A to 5D show different method stages of a further method varianton the basis of schematic cross sections;

FIGS. 6A to 6C show a measure for hermetic sealing on the basis ofdifferent method stages during the production of a MEMS component;

FIGS. 7A to 7C show the production of a structured metallization and ofa passivation layer on the basis of different method stages;

FIGS. 8A to 8C show different method stages during the production of astructured metallization;

FIGS. 9A and 9B show two method stages during the production of onevariant of a metallization structure; and

FIG. 10 shows a plan view of the active surface of a substrate withactive component structures, contact areas and frame structure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows in schematic cross section an individual substrate for aMEMS component at a stage in which the substrate SU is connected to thecarrier layer TS with the aid of a resist layer RL. The substrate SU hascomponent structures BES on its active surface AS. The componentstructures additionally comprise contact areas (not illustrated in thefigure) on which metallic column structures PS are seated. Furthermore,a frame structure RS, preferably composed of the same material as thecolumn structures PS, is applied on the active surface AS. The framestructure encloses at least the active component structures BES on thesurface. The contact areas and column structures are also arrangedwithin the frame structure RS. However, it is also possible to arrangeindividual ones of the contact areas and of the column structures PSseated thereon outside the frame structure on the active surface AS.

With the metallic structures, namely the metallic frame structure RS andthe metallic column structures PS, the substrate SU is seated on aresist layer RL arranged on a carrier layer TS. In this case, it is atleast ensured that the cavity CV within the frame structure RS betweensubstrate SU and carrier layer TS is totally sealed. This presupposesthat the metallic structures at least dip into the resist layer RL. Theresist layer is preferably a UV-curable resist layer. The thickness ofthe resist layer is chosen to be smaller than the height differencebetween the component structures the highest column structures.

The metallic structures can penetrate into the resist layer RL to adepth such that they come into contact with the surface of the carrierlayer TS.

FIG. 2 shows such an embodiment in which only a portion of the metallicstructures have penetrated into the resist layer RL as it were to a stopat the carrier layer. Such a differentiation between the metallicstructures is achieved by virtue of the more deeply penetrating metallicstructures being thickened with an additional metal ply AM, which can bestructured differently in comparison with the lower first metal ply. Ina manner illustrated in combined fashion in a single illustration, FIG.2 shows, e.g., further metal plies AM0 having the same cross section asthe underlying first metal ply. Furthermore, it is possible to choosethe cross section of the further metal ply within a column structure tobe larger than the cross section of the first metal ply, as isillustrated for the further metal plies AM1. In a third variant, thecross section of the further metal ply AM2 can have a smallercross-sectional area than the underlying first metal ply of therespective column structure PS.

A widened second metal ply AM1 has the advantage that it ensures anincreased method reliability during the later contacting through thecarrier layer TS. A narrowed second metal ply AM2 has the advantage thatit can be sunk into the resist layer R11 more easily. The metallicstructures which are not thickened with a second metal ply AM andtherefore have a smaller height than the thickened metallic structurescannot penetrate as far as the surface of the carrier layer TS. Inparticular, metallic structures which are not provided for electricalcontacting can remain without a second metal ply.

FIGS. 3A to 3C show different method stages during the production of aMEMS component in accordance with a further variant or embodiment, whichmanages without a carrier layer TS in the end product. FIG. 3A shows acarrier substrate TS coated with a resist layer RL, and a substrate SUhaving component structures, a frame structure RS and column structuresPS. The metallic structures can have identical or different heights. Itis advantageous if the surfaces of the metallic structures are broughtto the same level with the aid of a planarization process, for example,by milling away or grinding away, such that their surfaces lie withinone plane and can thus be better covered tightly with a planar carrierlayer TS.

FIG. 3B shows the emplaced substrate SU, wherein the metallic structureshave penetrated into the resist layer RL as far as the surface of thecarrier layer TS. Afterward, the resist layer RL is cured and preferablyirradiated with UV light for this purpose.

After the resist layer has been cured in this way to form a UV-curedresist, the impermeability of the cavity CV is ensured, as is themechanical stability thereof. It is then possible to strip the carrierlayer TS away from the cured resist layer, such that only the curedresist layer RL remains at the component. The top sides of the metallicstructures terminate flush with that surface of the resist layer RLwhich faces away from the substrate, that is to say that they areexposed and can thus be contacted in a simple manner. FIG. 3C shows thearrangement in this method stage.

A residual layer thickness of the resist layer RL which is possiblystill present over the ends of the metallic structures can be removed inan additional method step mechanically, chemically or in some other way,for example, by plasma etching.

FIGS. 4A and 4B show two method stages during the production of acomponent in accordance with a further variant. In contrast to thevariants according to FIGS. 1 to 3, here the resist layer RL is notapplied as a whole-area layer on the carrier substrate TS, but rather inaccordance with FIG. 4A selectively only on those ends of the metallicstructures which face away from the substrate. This is accomplished bymeans of a suitable method, for example, by means of an, e.g.,UV-curable resist being applied by printing, spreading or rolling.

FIG. 4B shows the arrangement after the metallic structures covered withthe resist layer RL have been placed onto the carrier layer TS. In thisway, too, the cavity CV can be tightly closed off. For this methodvariant, however, it is advantageous to bring all the ends of themetallic structures to the same level by means of the abovementionedplanarization method, in order more reliably to ensure theimpermeability of the cavity CV.

FIGS. 1 to 4 illustrate the components in method stages before astructured metallization for producing external contacts and for makingcontact with the active component structures BES is applied. In allthese embodiments, the minimum layer thickness of the resist layer RL ischosen such that the cavity CV can be tightly closed off, which overallis additionally a question of the structure accuracy and the planarityboth of the metallic structures and of the carrier layer TS. Theembodiment wherein the carrier layer TS is removed additionally requiresa higher layer thickness of the resist layer RL, since the latter isused as a self-supporting component covering or as a housing cover andin this case must ensure the mechanical stability of the covering. Atypical layer thickness for a variant according to FIG. 2 is 1 μm, forexample. A suitable layer thickness for the variant according to FIG. 3is 10 μm, for example. Under the abovementioned prerequisites of themethod reliability, the impermeability of the cavity and the goodadhesion, a suitable layer thickness can, however, deviate from thesevalues upward or downward.

FIGS. 1 to 4 illustrate the component and the method leading thereto onthe basis of an individual component substrate and the correspondingsection of the carrier layer TS, but said method is generally carriedout simultaneously at the wafer level for all components situated on awafer.

FIGS. 5A to 5D show further details during production at the waferlevel. A wafer serving as substrate SU comprises active componentstructures for a multiplicity of components. Active component structuresand metallic structures of a respective component are arranged within acomponent region BB, of which the wafer serving as substrate SU has amultiplicity. A trench pattern GM introduced into the active surfacecomprises trenches enclosing each individual component region BB alongthe later separation line in the singulation of the components. Thetrench pattern can be introduced into the substrate SU to approximately50% of the layer thickness. The minimum depth of the trench pattern GMcorresponds to the final layer thickness of the substrate provided forthe later component after thinning.

The metallic structures are preferably leveled by means of theabovementioned planarization method, such that a resist layer can beapplied to the upper ends of the metallic structures in a simple mannerby means of a printing method. A resist layer applying device RAtherefore comprises a roller, for example, which can be used for rollercoating. The resist is applied to the surface of a roller and rolledonto the metallic structures. FIG. 5A shows the arrangement during theapplication of the resist layer RL.

In the next step, the carrier layer TS is placed onto the metallicstructures coated with resist. For this purpose, a thin and flexiblefilm is preferably used, which be a plastic film, a composite filmcomprising plastic and a further material, in particular inorganicmaterial, or a purely inorganic film and consist of glass, for example.Hermetic materials, for example glass, are preferred.

The flexible carrier layer TS or the film used therefor is then rolledor laminated onto the metallic structures of the entire wafer with theaid of a carrier layer applying device TA. Suitable pressure ensures areliable connection of carrier layer TS and metallic structures thatguarantees a reliable closure of the cavity. FIG. 5B shows thearrangement during the application of the carrier layer TS.

In the next step, the layer thickness of the wafer serving as substrateSU is reduced from the rear side. This can be carried out by means ofgrinding away, for example. The thinning is carried out until the trenchpattern is exposed from the rear side of the substrate SU. In this way,the individual substrates are separated from one another, such that eachcomponent region BB has a substrate mechanically separated from adjacentcomponents. FIG. 5C shows the arrangement at this method stage, wherein,however, in contrast to FIGS. 5A and 5B, now the substrates areillustrated facing upward.

If a hermetic carrier substrate TS is used, then in a further methodstage the hermeticity of the components can be increased further byvirtue of the separating joints between the metallic structures, inparticular the frame structure, and the carrier layer being covered witha hermetic layer. For this purpose, through the trench pattern, or thegaps existing between the individual component regions BB, hermeticmaterial is thus applied to the exposed surfaces of the carrier layer,of the resist layer and at least portions of the frame structure. Thiscan be carried out by means of an isotropic application method that issuitable for producing a layer also at vertical or overhanging surfaces.However, it is also possible to use a structuring anisotropic method,for example, a jet printing method. This makes it possible to produceeven fine structures of the printed material at the desired location.The application of the hermetic layer HS is indicated by arrows in FIG.5D.

Inorganic layers, in particular metallic layers, serve as the hermeticlayer. The jet printing method can also be used to print inks whichcomprise metallic particles and which can be converted into continuousand impermeable metallic coatings. Inks which comprise metallicnanoparticles can be melted at particularly low temperatures andconverted into continuous metal layers or metal structures. Such inkscomprise silver nanoparticles, in particular.

A hermetic layer HS applied in a structured fashion or applied bysputtering over the whole area can additionally be reinforced by anelectrolytic or electroless metal deposition method and theimpermeability of said hermetic layer can thereby be increased. Ahermetic layer HS also applied to the rear sides of the substrates overthe whole area can additionally exhibit a shielding action againstelectromagnetic radiation.

Through the gaps between the individual substrates, regions of theresist layer RL that are exposed there can be removed by means ofetching. This is indicated by arrows in FIG. 6A. FIG. 6B shows thearrangement after the removal of the resist layer RL between theindividual components, such that the surface of the carrier layer TS isexposed there.

In these regions, a hermetic layer is then deposited, as described abovewith reference to FIG. 5. This can be carried out selectively in theregion between the substrates, as illustrated in FIG. 6C, or elsealternatively over the whole area over the entire arrangement and therear sides of the substrates SU.

FIGS. 7A to 7C show different method stages during the production of astructured metallization on that surface of the covering which facesaway from the substrate, said covering here being illustrated as a pureresist layer RS in accordance with the method variant according to FIG.3. FIG. 7A shows the component after placement onto the carrier layercovered with a resist layer over the whole area, in such a way that theends of the metallic structures completely penetrate through the resistlayer and are practically in contact with the carrier layer TS. Afterthe resist layer has been cured and the carrier layer has been strippedaway, the surfaces of the metallic structures are therefore exposed atthe outwardly facing surface of the resist layer RL. By applying astructured metallization, it is then possible to produce connectinglines and external contacts HK. Metallization and structuring methodsknown per se are suitable for this purpose. In a simple manner, suchcontacts can, for example, be applied by printing and, if appropriate,reinforced by metal deposition. However, a two-stage metallization withthe aid of a metallic growth layer applied by sputtering and subsequentelectrolytic or electroless reinforcement is also possible. FIG. 7Bshows the arrangement at this method stage.

In the next step, that surface of the resist layer RL which is providedwith external contacts AK can also be provided with a passivation layerPS. Such a passivation layer is preferably produced from inorganicmaterial, in particular an oxidic, nitridic or other hard andimpermeable material. The passivation layer PS is structured such thatit covers exposed regions of the resist layer and of the edges of theexternal contacts and only leaves free that region of the externalcontacts which is utilized for contacting purposes. FIG. 7C shows thearrangement with the applied and structured passivation layer PS. Theexternal contacts can be produced in the form of a ball grid array or aland grid array in a manner known per se.

FIGS. 8A to 8C show different method stages during the production of astructured metallization on the outwardly facing underside of thecarrier layer TS. FIG. 8A shows the arrangement after a carrier layer TScovered with a resist layer RL has been placed onto the metallicstructures of the component substrate SU. After curing by means of UVlight and conversion into a UV-cured resist layer RL, blind holes SL areproduced from the underside of the carrier layer, in which blind holesthe surface of the metallic structures to be contacted are exposed. Theblind holes are produced such that the enclosed cavity CV remainsclosed, that is to say that the resist layer RL is not penetrated by theblind hole. Various measures are suitable for this purpose.

By way of example, it is possible to monitor the layer depth. A furthermeasure comprises end point identification, wherein the beginning of theremoval of the metallic structure is identified. A further possibilityconsists in centering the cross-sectional area of the blind hole SL ineach case on the metallic structure to be contacted, and in making thecross-sectional area of the blind hole smaller than the cross section ofthe metallic structure, such that the base of the blind hole SL isformed completely by the metallic structure. In this way, the metal ofthe metallic structure constitutes a “natural” etching stop.

A suitable method for producing the blind holes SL can be chosendepending on the material of the carrier layer TS. If the carrier layerTS has a sufficiently thin layer thickness, the blind holes SL can beproduced with the aid of a laser. This has the advantage that the lasercan be used positionally accurately and an additional resist mask is notrequired. Also suitable are dry or wet etching methods which must can becarried out using a corresponding resist mask that is applied on theunderside of the carrier layer TS and is structured.

In the next step, a structured metallization MS is produced such that itcan be electrically conductively connected to the metallic structuresexposed in the blind holes. For this purpose, as illustrated in FIG. 8C,for example, an electrically conductive material, in particular a metal,is deposited preferably over the whole area, for example, by sputtering,such that it is in contact with the metallic structure at the base ofthe blind holes. This is followed by structuring and, if appropriate,reinforcement of the metal layer in a metal deposition method, which canbe carried out electrolytically or in an electroless fashion. Thestructuring can be carried out by applying a structured resist mask tothe metal layer applied over the whole area, such that the thickeningtakes place only in the regions remaining free of the resist mask.Afterward, the mask is removed and the residues of the metal layer inthe non-reinforced regions are removed. FIG. 8C shows the arrangement inthis method stage.

However, it is also possible, after the method stage illustrated in FIG.8B (after the production of the blind holes SL), firstly to provide theblind holes with an electrically conductive filling, as is illustratedin FIG. 9B, for instance. This can be carried out by means of amechanical method, e.g., by introducing a conductive paste. Afterward,the structured metallization can be implemented in a layer depositionmethod on the carrier layer TS, which is now approximately planarbecause it is provided with filled blind holes SL.

However, it is also possible to apply the structured metallization bymeans of a printing method which can be performed such that it leads tothe contacting of the metallic structures including in the base of theblind holes.

FIG. 9A shows one variant of the method described with reference toFIGS. 8A to C, wherein the metallic structures are embodied with a crosssection that varies over the height. In the embodiment illustrated, atleast in the case of a portion of the metallic structures RS, PS, theupper end remote from the substrate is provided with a largercross-sectional area, which is then pressed into the resist layer RL asfar as the contact with the carrier layer TS upon placement of thesubstrate. The enlarged cross-sectional area of the metallic structureshas the effect that more area is available for producing the blindholes, without the enclosed cavity being opened as a result. A blindhole reliably centered on the widened cross section of the metallicstructures leads to high method reliability.

The cross-sectional area of the metallic structures can be varied duringthe production of the metallic structures in a step between first andsecond metal plies. In the present example, the further metal ply AM1 isproduced above specific metallic column structures PS to be contactedwith a larger cross-sectional area than the first metal ply.

FIG. 9B shows a structured metallization wherein the blind hole SL isclosed with an electrically conductive compound CF. The structuredmetallization then comprises the electrically conductively filled blindhole and a metallization applied on the underside of the carrier layerover the filled blind holes, said metallization realizing externalcontacts AK.

FIG. 10 shows in plan view a substrate with component structures BES,contact areas KF connected thereto, or with metallic column structuresPS seated thereon and with a frame structure RS enclosing the componentstructures. A dash-dotted line denotes the substrate edge, or theboundary of the component region BB which can be formed together with aplurality of further component regions and the associated structures ona common wafer. An interdigital transducer such as is used as afrequency-determining structure in SAW components, for example, isillustrated in a representative manner for the component structures BES.The component structures BES can also comprise further structures orfurther interdigital transducers besides the interdigital transducer.Other types of electrical or electromechanical components can also havecomponent structures deviating therefrom, for example, a movablemembrane in a capacitive MEMS component.

The frame structure RS encloses the component structures BES. In adeparture therefrom, however, the contact areas KF can be led, by meansof a lead running below the frame structure RS, into a region outsidethe region enclosed by the frame structure RS. Since neither contactarea nor metallic column structure constitutes a mechanically sensitivestructure, these also need not be arranged in the cavity enclosed by theframe structure RS in the finished component.

Insofar as only individual components have been illustrated in theembodiments illustrated and described above, it is nevertheless clearthat all the method steps are preferably carried out at the wafer level.The invention has been illustrated in part on the basis of only anindividual substrate for a single component merely for the sake ofsimplicity. Individual structures illustrated in the figures can also beused in other embodiments, even if they are not explicitly mentioned orillustrated therein. In this regard, it is possible, for example, toprovide in all embodiments a hermetic layer which covers at least theside surfaces of the component and closes them off relative to thecarrier layer TS. The hermetic layer HS can also cover the entire rearside of the substrate SU. Furthermore, the hermetic layer can beelectrically conductively connected to an external contact AK on theunderside of the carrier layer TS via a correspondingly positionedcontact hole.

It is also possible in all cases to make electrical contact with theframe structure RS, preferably to connect it to a grounded externalcontact AK. With the aid of this additional ground connection, animproved shielding of the component is achieved, which provides forinterference-free operation of the component.

If individual method step have been described on the basis of specificmethods known per se, the method is nevertheless not restricted to thisexpressly mentioned means, provided that other methods having anidentical action are known and can be used.

For all components together with encapsulation manufactured at the waferlevel, it holds true that they generally have to be singulated by thesevering of the carrier layer in a final or in one of the final steps.Furthermore, it is possible for the individual components, as early atthe wafer level, to be covered with a mechanically stable pottingcompound in addition or as an alternative to the hermetic layer, inorder to facilitate secure handling of the component. A potting compoundapplied at the wafer level requires a separate singulation step in orderto sever the not inconsiderable layer thickness of the potting compoundin the region of the separation lines separating the component regionsBB.

The invention is not restricted to the exemplary embodiments describedand illustrated in the figures. Rather, all novel features and featurecombinations in particular of features mentioned in the claims should beregarded as associated with the invention.

The invention claimed is:
 1. A Microelectromechanical Systems (MEMS)component comprising: a substrate having an active surface, whereinelectrical component structures and contact areas for making electricalcontact with the electrical component structures are arranged on thesubstrate; metallic column structures located on the contact areas andprojecting beyond the electrical component structures; a metallic framestructure arranged on the active surface of the substrate and enclosingthe electrical component structures together with the metallic columnstructures; a resist layer seated on the metallic frame structure andthe metallic column structures such that the substrate, the metallicframe structure and the resist layer form an enclosed cavity, wherein atleast one portion of selected metallic column structures and themetallic frame structure penetrates through the resist layer to anextent such that those surfaces of the metallic column structures thatface away from the substrate are not covered by the resist layer; and astructured metallization arranged over a surface of the resist layerthat faces away from the substrate, wherein the structured metallizationforms at least structured external contacts for making contact for theMEMS component and are electrically conductively connected to thesurfaces of the metallic column structures not covered by the resistlayer.
 2. The MEMS component according to claim 1, further comprising afurther carrier layer arranged on the resist layer, the structuredmetallization being arranged on the further carrier layer.
 3. The MEMScomponent according to claim 1, wherein a carrier layer is arrangedabove the resist layer; wherein the structured external contacts arearranged on the surface of the carrier layer; and wherein plated-throughholes through the carrier layer are provided that connect the externalcontacts to the metallic column structures.
 4. The MEMS componentaccording to claim 3, wherein a hermetic layer seals a rear side of thesubstrate, the rear side being located opposite the active surface,relative to the carrier layer.
 5. The MEMS component according to claim4, wherein the substrate is a piezoelectric wafer; wherein theelectrical component structures comprise an interdigital transducer;wherein the carrier layer is a glass film; and wherein the hermeticlayer is a metallic layer.
 6. A Microelectromechanical Systems (MEMS)component comprising: a substrate having an active surface withelectrical component structures and contact areas; metallic columnstructures located on the contact areas; a metallic frame structurearranged on the active surface of the substrate and enclosing theelectrical component structures and the metallic column structures; aresist layer seated on the metallic frame structure and the metalliccolumn structures such that the substrate, the metallic frame structureand the resist layer form an enclosed cavity, wherein selected ones ofthe metallic column structures penetrate through the resist layer suchthat surfaces of the selected metallic column structures that face awayfrom the substrate are not covered by the resist layer; and a structuredmetallization arranged over a surface of the resist layer that facesaway from the substrate, wherein the structured metallization forms atleast structured external contacts for making contact for the MEMScomponent and is electrically conductively connected to the surfaces ofthe metallic column structures.
 7. The MEMS component according to claim6, further comprising a carrier layer arranged on the resist layer, thestructured metallization being arranged on the carrier layer.
 8. TheMEMS component according to claim 7, wherein the substrate is apiezoelectric wafer, wherein the electrical component structurescomprise an interdigital transducer, and wherein the carrier layer is aglass film.
 9. The MEMS component according to claim 6, furthercomprising: a carrier layer arranged on the resist layer; structuredexternal contacts arranged on the surface of the carrier layer; andthrough holes located in the carrier layer such that the through holesconnect the external contacts to the metallic column structures.
 10. TheMEMS component according to claim 9, further comprising a hermeticlayer, wherein the hermetic layer seals a rear side of the substrate,the rear side being located opposite to the active surface.
 11. The MEMScomponent according to claim 10, wherein the substrate is apiezoelectric wafer, wherein the electrical component structurescomprise an interdigital transducer, wherein the carrier layer is aglass film, and wherein the hermetic layer is a metallic layer.
 12. TheMEMS component according to claim 6, further comprising a hermeticlayer, wherein the hermetic layer seals a rear side of the substrate,the rear side being located opposite to the active surface.
 13. AMicroelectromechanical Systems (MEMS) component comprising: a substratehaving an active surface with electrical component structures andcontact areas; metallic column structures located on the contact areas;a metallic frame structure arranged on the active surface of thesubstrate and enclosing the electrical component structures and themetallic column structures; a resist layer seated on the metallic framestructure and the metallic column structures such that the substrate,the metallic frame structure and the resist layer form an enclosedcavity, wherein the resist layer has an interface with the enclosedcavity; and a structured metallization arranged over a surface of theresist layer that faces away from the substrate, wherein the structuredmetallization forms at least structured external contacts for makingcontact for the MEMS component and is electrically conductivelyconnected to the metallic column structures.
 14. The MEMS componentaccording to claim 13, further comprising a carrier layer arranged onthe resist layer, the structured metallization being arranged on thecarrier layer.
 15. The MEMS component according to claim 14, wherein thesubstrate is a piezoelectric wafer, wherein the electrical componentstructures comprise an interdigital transducer, and wherein the carrierlayer is a glass film.
 16. The MEMS component according to claim 13,further comprising: a carrier layer arranged on the resist layer;structured external contacts arranged on the surface of the carrierlayer; and through holes located in the carrier layer such that thethrough holes connect the external contacts to the metallic columnstructures.
 17. The MEMS component according to claim 16, furthercomprising a hermetic layer, wherein the hermetic layer seals a rearside of the substrate, the rear side being located opposite to theactive surface.
 18. The MEMS component according to claim 17, whereinthe substrate is a piezoelectric wafer, wherein the electrical componentstructures comprise an interdigital transducer, wherein the carrierlayer is a glass film, and wherein the hermetic layer is a metalliclayer.
 19. The MEMS component according to claim 13, further comprisinga hermetic layer, wherein the hermetic layer seals a rear side of thesubstrate, the rear side being located opposite to the active surface.